What year and is it S-15 or FS.
I know from experience on an S-10/S-15 if it didnt come from the factory equipped with a tire carrier you can retrofit a factory one on without possibly screwing up the structure around the tailgate. Theres a couple structural braces that are in the way of the bolts and fasteners that go inside the quarter panel. The fasteners were captured by tack welds when the vehicle was manufactured and it's almost impossible to get up in there to get them in the correct place.
In the long run you'll be better off with an aftermarket one.